1. Field of Invention
The present invention relates to a position feedback control architecture of a linear actuator, and more particularly, to a method and apparatus for estimating the position of a moving part of a linear actuator.
2. Description of Related Art
The conventional position actuator generally employs a stepper motor as the driving device. However, stepping motors have many limitations. For example, the position speed is not fast enough, which is time and power consuming for the system when the position is achieved at a low speed; and relatively high mechanical noise occurs during position operation. Therefore, in order to improve the position properties and to efficiently reduce the hardware cost, a position feedback control through the linear actuator along with the magnetic scale has become the future trend.
FIG. 1 shows a position feedback control architecture for a conventional linear actuator. In the architecture of FIG. 1, when the moving part of the linear actuator 103 moves, a magneto-resistive sensor (MR sensor) 104 generates two magnetic signals with a phase difference of 90 degrees. The mixed-signal interpolation chip 105 converts the magnetic signals into pulse signals to be counted by a counter 106. Then, the counter 106 sends the counted values to a microprocessor 101, so as to obtain the position of the moving part of the linear actuator 103. The main defect of this architecture lies in that the price of the mixed-signal interpolation chip 105 is extremely high.
FIG. 2 depicts another type of position feedback control architecture for a conventional linear actuator 103 without the mixed-signal interpolation chip 105. In the architecture of FIG. 2, an analog-to-digital converter (ADC) 202 converts the magnetic signals from the MR sensor 104 into digital sample values, and then sends them to a microprocessor 201 to be analyzed, so as to estimate the position of the moving part of the linear actuator 103. This architecture utilizes an algorithm implemented by the microprocessor 201 instead of the expensive mixed-signal interpolation chip 105. However, the conventional algorithms all require complicated and redundant computations, and require much time for floating-point computation, which adversely influences the position efficiency.